US1983364A - Superheater - Google Patents

Description

Dec; 1934. c. w. GORDON SUPERHEATER Filed Feb, 15, 1954 2 Sheets-Sheet 1 INVENTOR C/M/WEJ M GoEDoM QK'ZCJLCL ATTORNEY Filed Feb. 15, 1934 2 Sheets-Sheet 2 INVENTOR (Vi/F465 MK 60/900.

ATTORNEY Patented Dec. 4, 1934 SUPERHEATER Charles W. Gordon, Munster, Ind., assignor to The- Superheater Company, New York, N. Y.

Application February 15, 1934, SeriaLNO. 711,330

7 Claims.

This invention relates to steam superheaters. In' modern boiler practice a steam superheater comprises a plurality of tubular elements or units, the two ends of each of which are con- -nected: respectively to a steam inlet header and a steamoutlet header, the flow through the elements therefore being in parallel. Each of the tubular elements is made up of two or more straight parallel tube lengths-connected by the 10. necessary number of return bends to form a continuous conduit. These return bends can be made and applied in a-number of different ways. In some. forms they are made separately and subsequently connected to the pipes, and in other 15, cases they are made directly from the material of. the pipes themselves which are to be connected. The best method known to me for making them. directly from the pipe material is one involving a forge-weld and known in the trade as the Elesco method, which is fully described ina number of prior patents, for example United States Patent #1,155,109 and #l,169,209. This method may be-briefly described here as follows: Thetwo pipes to be connected by a return bend are first clamped together inthe relative position they are to occupy in the finished product, their ends are then heated to the proper welding temperature, the Walls which face each other are then, by means of suitable dies, split or slit- 30. ted inward from-the end for a suitabledistance, the portions of the pipe walls adjacent to the slits are bent outward into parallel position, the edges'of these bent-out flaps of one coming into forcible contact with the corresponding edges 35, of theother, whereby the edges of the one become forge-welded to the edges of the other, after which the open end of the incomplete return bend so formed is closed, thereby completing the structure. Ordinarily, a final shaping of 40, the structure is performed after such final cloployed. Cases are not uncommon and. will be. less so in the future in which the superheat of j the steam is carried to 1000 F. andevenhigher, and in such cases materials must be used for the superheater elements other than ordinary} carbonsteel; It has been found that with steam temperatures approximating or exceeding 1000 F. and with the elements exposed to the heating gases, the elements are attacked on the inside. The cause for this is not definitely known but it is probably due either to thepresence ofsome atmospheric air; in thesteamor to dissociation of the steam itself, the oxygen in either case attacking themetal.

The-obvious remedy is to employ materials that will; resist such oxidation. This may be either tubing made up non-oxidizing" alloys, or carbon steel tubing which has been given a protective coating the best one of which is furnished by the process known as calorizing.

Unfortunately, the method of making the re turn'bends outlined above cannot be employed with tubing of either of these two kinds, the reason being that neither of them will readily forge-weld. Return bends-with the coated tub ing can be made by the method mentioned, but only if either the coating'isremoved from those portions involved in making the return'bends or if-these ends are protected during-the calorizin'g process so that they remain uncoated; To make the entire element immune to corrosion such return bends would after their formation have to be calorized by a separate process, Another method ofprocedure would be to calorize' the entire element after fabrication. These two methods are feasible with elements comprising a single loop, i. e. two straight lengths connected by a single returnbend. The cost, however, is"pro-- hibitive. When the element comprises more than two loops, the coating after fabrication either of the entire element or of the return bends alone is practically impossible.

There are of course other methods of making return'bends utilizing the material of the pipes themselvesdirectly." One of them consists inpre,-' paring the two halves of the proposed return bend in muchthe same way as in the process-above described, i: e; slitting such end inwardly for the required distance and spreading the adjacent flapsoutward, the two pipes. being then fiash welded together electrically. This is entirely feasible with alloy tubing. It is, however, several" timesas expensive a process as the Elesco method.

' The same is' true offurther known methods of 7 making such return bends, whether madev directly from the pipe materlal or made'o'f separate pieces subsequently welded to the pipes. They areall materially higher in cost than the Elesco method andin many cases less'satisfa'ctory.

By inventionthe Ele'sco method of making return bends can be used even in cases where the steam temperature is in the neighborhood of 1000 F. and the provision of an arrangement whereby this method can still be used is the principal object of my invention.

I accomplish this object as follows: I take tubing of such quality that it will resist the conditions mentioned. This may be either tubing of suitable alloy steel or tubing which has been given a protective coating by calorizing or by any other preferred method. If alloy steel is used, I weld, preferably by an electric fiash method, to the ends of the tubes to be connected by a return bend lengths of ordinary carbon steel tubing sufiicient for the formation of return bends. With these lengths I then form by the forge-weld method described return bends connecting the pipes.

If coated tubing is used, I take precautions in the first place to prevent the ends of the tubing which are to be joined from becoming coated or alternatively remove the coating from such ends. I can as a further alternative also weld suitable uncoated carbon steel lengths to such coated tubes. The pipes are then connected by return bends in the ordinary manner.

Such units will then be able to resist attack on the inside with steam up to temperatures of 1000 F. and over and with heating gases or radia- -tion supplying additional heat on the outside,

thus raising the metal temperature higher than the steam temperature, this, however, being true only for the alloy or coated portions and not being true for the return bends. These return bends,

if exposed to heating gases and thereby having the metal temperature raised materially above the steam temperature, would be attacked on the inside as described. I have found, however, that these return bends are entirely capable of resisting steam temperatures of 1000 and over provided they are not exposed on their outer sides to further heating by convection or radiation. The wall temperature of the return bends must, in other words, be kept from rising above the steam temperature.

I can accompiish this in different ways, two of which are illustrated in the drawings filed herewith. In these drawings Fig. 1 shows a boiler of the four-drum type with the superheater arranged in accordance with my invention. Fig. 2

shows a cross drum horizontal tube boiler with a radiant type superheater embodying my invention. Fig. 3 is a section on line 3-3 of Fig. 2 and Figs. 4 and 5 illustrate details of the return bend, the former in an unfinished stage and the latter completed.

Referring first to Figs. 4 and 5, tubing made of suitable alloy, or suitably coated, is shown at 1-1, these being the ends of two straight superheater tube lengths which are to be joined by a return bend. To the ends of these lengths have been connected preferably by a fiash weld lengths 22 of ordinary steel tubing. Fig. 4 shows these two lengths 22 connected by an incomplete return bend, this being an intermediate stage in the Elesco method. 5 shows the same structure with the return bend completed, i. e. its end closed at 3. Ordinarily, the main portions of the straight lengths are separated further in the finished superheater element than they appear in Fig. 4. In Fig. 5 this is indicated by the offsets 4-4.

Referring now to Fig. 1, the boiler used for illustrative purposes comprises the usual upper drums 5,6 and 7 and the lower drum 8, the latter connected to the upper drums by banks of tubes 9, 10 and 11. The upper drums 5 and 6 are connected to each other by circulators 12 and the three upper drums are connected by steam tubes 13-13. Baiiiing 12a covers the circulators 12.

The superheater inlet header 14 receives its steam from the steam drum '7 by means of the steam pipe 15. The superheater is located be-- tween the front bank of tubes 9 and the middle bank 10. Only one element 16 is visible, the other elements being in alinement behind or in front of it. The elements are each connected with one end to the inlet header 14 and with their other ends to the outlet header 17.

Tubing is available obviating the necessity of fabricating return bends at the lower end. As shown at 19-19, the tubes are merely bent, this being done by any preferred method.

It thus becomes necessary in a unit of four loops such as that illustrated to make only three return bends l818. The feature of my invention which makes the use of ordinary carbon steels for these return bends 1818 possible is that I locate these return bends in a place where they are exposed to no external heating. In the form of Fig. 1 this is accomplished by extending the units upwardly so that these return bends lie in the space above the circulators 12 and the bafiie 12a. In this location they are protected against external heating and their metal temperature will be that of the steam and they are under these conditions entirely capable of re-v sisting steam temperatures up to and even exceeding 1000 F. V

In Fig. 2 the application of my inventive idea to a radiant type superheater is shown. The boiler is of an ordinary cross drum type, steam from the drum 18 being led by means of steam pipe 19 to the inlet header 20. One end of each element is connected to this inlet header, its other end being connected to the outlet header 21. One of the superheater elements appears at 22 and it will be noted that it comprises two straight lengths lying adjacent to the Wall 23 of the setting. It will be obvious that while the illustrated form has single-loop elements, there may at times be more than one loop to each element. Preferably, a row of protective water tubes 24 is, in accordance with prior practice, arranged between the row of superheater elements and the furnace.

The return bends 1811., each connecting apair of lengths 22, are in this form protected by being placed within the wall 23, the upper ends of the lengths 22 being for this purpose bent at right angles at 25. Preferably the return bends are located in a cavity or cavities 26 in the wall 23 so that the units can still be readily removed and replaced.

Other means of affording the desired protection for these return bends can evidently be used both in this radiant type of superheater and in the form first described. In other forms of boilers means different from those illustrated and described herein will readily suggest themselves and perhaps be even preferable. As long as the condition is met that the main part of the element is made of heat-resistant material while the return bends are of ordinary material, and that no, or substantially no, external heating occurs at the return bends, such structures fall within the scope of myinvention.

What I claim is:

l. A'tubular steam-superheating element for use under conditions such that the steam flowing iii through the element is raised to a temperature of 950 F. or above, comprising a plurality of lengths of tubing exposed to external heating and return bends joining said lengths and protected from said heating, the materials of the tube lengths and return bends being such respectively that the former are and the latter are not adapted to resist, in the presence of steam of said temperature, metal temperatures resulting from exposure to said external heating.

2. A tubular steam-superheating element comprising two pipe lengths connected by means of a forge-welded return bend, the pipe lengths being made of material which is highly resistant to oxidation when heated but not readily forgeable, the return bend being made of material less resistant to oxidation when heated but readily forge-welded, means to cause steam to flow through the element, means to expose the outside of the pipe lengths to intense heat, and means to protect the return bend against such heat.

3. A superheater comprising a plurality of elements each constituted and arranged in accordance with claim 1.

4. A superheating element in accordance with claim 1, the return bends being protected by being located in a dead space shut ofl from radiation and gas circulation.

5. A superheating element in accordance with claim 2, the return bend being protected by being placed within a wall of the boiler setting.

6. The process of making a tubular superheatingelement comprising the steps of welding relatively short lengths of tubing made of material which can be forge-welded to lengths of tubing which cannot readily be forge-welded, and assembling the resulting compound tubes into continuous tubular elements by uniting the short lengths in pairs into return bends by a forge method.

7. The process according to claim 6, the short lengths being welded to the lengths of tubing by an electric flash method.

CHARLES W. GORDON.

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